This invention relates generally to semiconductor processing technology and more particularly the invention relates to dielectrics used in submicron devices as used in ULSI microelectronic circuits.
The metal-insulator-silicon (MIS) transistor including the metal-oxide-silicon (MOS) transistor is used in large scale integrated (LSI), very large scale integrated (VLSI), and ultra large scale integrated (ULSI) microelectronic circuits. The transistor has a current carrier source region formed in a surface of a semiconductor (e.g., silicon) body, a carrier drain region formed in the surface and spaced from the source, and between the source and drain is a channel region through which the current carriers flow. Overlying the channel region and aligned with edges of the source and drain is a gate electrode which is physically and electrically separated from the channel by a dielectric layer. Typically the dielectric comprises a silicon oxide (SiO.sub.2).
To provide stress relief and to enhance the electrical qualities of the dielectric, a silicon nitride (Si.sub.3 N.sub.4) layer has been placed over the silicon oxide layer between the gate electrode and the channel region. Additionally, nitride ions have been placed in the silicon oxide layer by ion implantation and by NH.sub.3 (anhydrous ammonia) nitridation.
However, NH.sub.3 nitridation incorporates hydrogen in the oxides, which increases electron trapping significantly. Reoxidation of nitrided oxides (ROXNOX) is unable to eliminate the nitridation induced electron traps, leading to worse hot carrier reliability of p-MOSFETs. Even in n-MOSFETs with ROXNOX SiO.sub.2, the hot carrier reliability is degraded under peak I.sub.g stress due to the presence of electron traps. Although the electron trapping problem can be reduced by using a very light nitridation, the resulting oxides do not show sufficient resistance to boron penetration. Consequently, (reoxidized) NH.sub.3 -nitrided gate oxides may not be adequate for p.sup.+ -polysilicon gated p-MOSFETs. On the other hand, alternatives to (reoxidized) NH.sub.3 -nitrided oxides, namely N.sub.2 O-nitrided and N.sub.2 O-grown oxides may not contain sufficient nitrogen atoms to prevent boron penetration.
The present invention is directed to an improved dielectric for use in deep submicron MOS devices and the fabrication thereof.